What percentage of the potential heat energy of the fuel does the modern diesel engine convert to kinetic energy when it is operating close to optimum efficiency?

In modern diesel engines operating near optimum efficiency, approximately 40% of the potential heat energy from the fuel is typically converted to kinetic energy. This conversion is a reflection of the efficiency of the engine in using the fuel's energy to do mechanical work.

The efficiency of diesel engines is generally higher than that of gasoline engines because of their high compression ratios and the inherent properties of diesel fuel, which allow for better energy extraction. Various factors contribute to this efficiency, including design aspects such as turbocharging, fuel injection timing, and after-treatment systems that enhance combustion stability and reduce waste energy.

As a point of reference, while other options suggest a range of efficiencies, 40% represents a realistic figure for well-designed diesel engines under optimal conditions, recognizing that not all the energy from the fuel can be converted into useful work due to thermal inefficiencies and other energy losses in the system, such as heat lost through exhaust and engine cooling.